Base-Promoted Reactions of Epoxides. II. 3,4- and 5,6-Epoxycyclooctene

Phosphorylation of alkyl-2-chloro-2,3-epoxyalkanoates with trialkyl phosphites: A novel approach to alkyl 2-diethoxyphosphoryloxy-2-alkenoates

“…An attack of phosphorus (III) compounds on chlorine or bromine of ␣-halobenzyl phenyl sulfones or ␣-bromoacetophenones and the formation of anions stabilized by adjacent sulfonyl or carbonyl group have been reported [13,14]. Also, ring openings of epoxy anions of the type 12 leading to enolate anions have been observed [15,16].…”

Organolithium/Chiral Lewis Base/BF3: a Versatile Combination for the Enantioselective Desymmetrization of meso‐Epoxides

“…This difference of behavior has been rationalized by Crandall [38] as a result of a steric decongestion of the carbocyclic ring, induced by the presence of the double bond, which may increase the flexibility and allows a suitable conformation for the postulated β-elimination process. [39] In the same manner, this steric decongestion could reduce the strain energy of the epoxide ring, thus decreasing the acidity of the α-proton. [32] Scheme 7.…”

Reactivity of Oxiranes with Organolithium Reagents

“…The presence of BF 3 in the reaction can also have an effect on the α-vs. β-deprotonation regioselectivity. The oxirane 83 (Scheme 70), when treated with the mixture s-BuLi/(−)-sparteine, leads to the cyclooctadiene alcohol 172 (through a β-deprotonation process 258 ), whereas in the same conditions but in the presence of BF 3 the bicyclic compound 166 is obtained (through an α-deprotonation process). Presumably, the high yield in the rearranged product 166 can be interpreted by the higher acidity of the oxiranyl protons in the presence of BF 3 , or by an enhanced carbenoidic character of the lithiooxirane intermediate, or both.…”